A temperature-controlled chamber has been constructed which can be placed in the viewing field of a light microscope. The microscope is used to visualize an individual cell within the chamber. An electrode is then inserted into the cell to measure its electrical activity. The feedback thermocouple for the temperature-control system is located near the cell under study. The temperature is then cycled between 37 degrees C and approximately 20 degrees C over the course of 1 minute. The lower temperature inhibits or turns off certain enzymes which affect the electrical activity of the cell. These changes are then observed.